I've just upgraded my male Betta from a 2.5 gallon to a 10 gallon tank, and so far he seem quite happy for the extra exercise. The fish that were in the tank before were taken back to the store since I wanted to make room for the Betta (he'd been in the 2.5 gallon since February, which I figured was long enough!). Two of the fish that were in there before, a platy and a guppy, had several fry, and the ones that didn't manage to get eaten are still in there because this is the first time I've had fry and I really wanted to watch them grow. There are two 3-week old guppies and I think three mickey mouse platy fry, only a few days old. The guppies are in a breeder's net at the moment, just in case, and the platy fry are hiding in the plants and inside a cave. I know they'll get big pretty fast and I do plan on either dividing the tank or giving them back to the store, but for now I'm wondering if they're safe? Will the Betta eat the smaller fry, if he can find them? So far he seems indifferent to them, but maybe he just hasn't fully noticed.

My betta is living with 6 guppies at the moment with no aggression. I really believe every fish has a different temperment and I got lucky. I do have a big castle cave that my betta seems to have claimed as his own and the guppies never go inside of it. There are also lots of real plants. I've tried a similar arrangement 2 other times in a different tank and with different bettas and no way was that going to work. Make sure the betta is added to the tank after the guppies have already been there.

Thanks, everyone. My main concern was whether or not he would eat the fry. When I put him in I had about three guppy fry in there which didn't seem small enough to be able to fit into his mouth. Alas, one has disappeared, and I assume he was eaten. :( So now there are two guppy fry and two platy fry safely in a breeding net. I'm hoping he'll get used to seeing them through the net, then if I let them out when they're bigger he'll be comfortable with having them around. The other option was to see if the two guppy fry would work in my other Betta's 5.5 gallon tank.
In the 10 gallon, on the other side of a divider, is an albino cory and a golden killi fish. The cory might get along with the Betta, from what I've read, but I don't know about the Killi.

Most of my betta's I own now, both females and males won't look sideways at young fry of any kind, It's only when the fry get older that Mine sometimes has mood swings., It's the female Betta's I have found to be the worse for getting into the wrong moods and nipping/ripping fins,

But that's not to say yours won't eat them, Every Betta has it own unique attitude. only way to know is try and see what happens.